In connection with the cleaning of the exhaust gases of vehicle engines operated with diesel fuel, e.g., of engines used to drive construction equipment, it is necessary to remove the soot particles from the exhaust gas. Removal of the soot particles by filtration has proved to be a particularly suitable cleaning method. According to this method, the exhaust gas is introduced into one or several filter elements, e.g., filter cartridges; the soot particles are retained on the surface of the filter during the passage of the exhaust gas through the filter and are deposited there. This exhaust gas cleaning by filtration requires the removal of the soot particles accumulated at certain intervals. It would be possible to do this by removing and collecting the soot particles, but this would require removal of the filter at regular intervals and removal of the soot accumulated according to accumulated according to another method. Consequently, this method is unsuitable for vehicles, e.g., trucks or passenger cars.
Cleaning by burn-off, i.e., burning off of the soot particles accumulated, has proved to be a better method. If this cleaning method is used, two groups of filters are preferably arranged in parallel to one another. Exhaust gas flows through one of the groups to filter the exhaust gas, while the other group is being regenerated by burning off the soot particles. To achieve this, a burner, e.g., preferably a burner known in connection with engine-independent heaters, is arranged on the intake side of the filter. To regenerate the filter, the necessary temperature is produced to start the burning off process, and the temperature can be reduced after burning off has started. In the case of engine-independent heaters, this happens in the prior-art devices by speed control of the side channel blower used as a combustion air blower. However, this regulation of the blower speed is rather complicated and expensive, because it requires additional compensating resistors, which leads to a significant loss of energy over the resistors and requires special heat dissipation.
A side channel blower for delivering supplementary air into the exhaust gas system of a motor vehicle equipped with a spark ignition engine to reduce the pollutant emissions, comprising an air intake opening and a forced air outlet opening of the side channel blower with a bypass channel between the suction side and the delivery side, is known from U.S. Pat. Specification No. 3,356,034 of 1967. In this prior-art side channel blower, the flow cross section of the bypass channel can be adjusted with a slide. The more widely the slide is opened, the larger is the amount of air returned to the suction side and the lower is inherently the output of the side channel blower. However, this side channel blower has the disadvantage that the amounts delivered and the pressure setting depend on the speed of the drive engine.